1. Field of the Invention
The present invention relates to a semiconductor device which functions as an integrator circuit and a method for driving the semiconductor device. In particular, the present invention relates to a semiconductor device in which electric charge accumulated in a capacitor of an integrator circuit can be held even when a power source is turned off and a method for driving the semiconductor device.
In this specification, a semiconductor device refers to a device including a semiconductor element. Therefore, integrator circuits which are to be described in this specification are semiconductor devices.
2. Description of the Related Art
An integrator circuit including a differential amplifier circuit (also referred to as an operational amplifier) is known as a circuit which is used for a loop filter or the like in a phase locked loop circuit (PLL circuit).
A basic circuit configuration of the integrator circuit is disclosed in Patent Document 1.